1. Field
The present disclosure relates generally to materials modification and, more specifically, to plasma-based material modification using a plasma source with magnetic confinement.
2. Related Art
Ion-based material modification is an important process used in semiconductor manufacturing. For example, ion-based material modification may be used to amorphize crystalline materials, alloy metals, densify or mix layers of materials, facilitate removal of materials, or introduce impurities into materials. During ion-based material modification, ions are accelerated to bombard the surface of a work piece (e.g., a semiconductor substrate). The ions may be positive or negative ions comprising species or elements that are chemically reactive or inert with respect to the surface of the work piece. The ions may thus modify the physical, chemical, or electrical properties of the surface of the work piece.
Currently, ion-based material modification is performed predominantly using beam-line ion implantation systems. In beam-line ion implantation systems, an ion beam is extracted from an ion source and filtered by mass, charge, and energy through a magnetic analyzer before being accelerated towards a work piece. However, as dictated by Liouville's Theorem, the transport efficiencies of the ion beam decrease with decreasing ion energy. Thus, for low energy processes, beam-line ion implantation systems suffer from low beam currents and thus require long processing times to achieve the required doses. Further, the cross-section of the ion beam is significantly smaller than the area of the work piece where only a fraction of the surface of the work piece may be treated at any given moment. Thus, the ion beam or substrate must be scanned to uniformly treat the entire surface of the work piece. As a result, beam-line ion implantation systems suffer from low throughputs for high dose, low energy implant processes.
Plasma-based material modification systems are an alternative to beam-line ion implantation systems. FIG. 1 depicts an exemplary plasma-based material modification system 100. Plasma-based material modification system 100 comprises plasma source chamber 102 coupled to process chamber 104. Plasma 106, which contains ions, neutral species, and electrons, is generated in plasma source chamber 102. Work piece 118 is supported by support structure 116 within process chamber 104. In this example, plasma-based material modification system 100 has one or more biased grids 120 positioned between plasma 106 and work piece 118 to extract ion beam 112 from plasma 106 and accelerate ion beam 112 to work piece 118. However, in other examples, plasma-based material modification system 100 may not include grids 120. Instead, work piece 118 may be biased at a potential and immersed in plasma 106 by support structure 116. Ions are thus accelerated from plasma 106 to work piece 118 across a plasma sheath formed between plasma 106 and work piece 118. In some cases, work piece 118 may be treated with both ions and neutral species from plasma 106. Currently, most conventional plasma-based material modification systems do not have grids.
Unlike beam-line ion implantation systems, plasma-based material modification systems do not utilize a magnetic analyzer to filter ions by mass or energy. Rather, the work piece is treated with ions directly from the plasma in close proximity. Thus, plasma-based material modification systems can treat a work piece at significantly higher ion currents than beam-line ion implantation systems. In addition, the plasma sources of plasma-based material modification systems may have cross-sectional areas that are larger than the area of the work piece. This enables a large portion of or the entire surface of the work piece to be treated simultaneously without scanning the work piece. Therefore, plasma-based material modification systems offer significantly higher throughputs for high dose, low current processes.
Convention plasma-based material modification systems, however, suffer from poor system reliability and process control. Due to the proximity of the plasma to the process chamber, neutral species from the plasma flow into the process chamber and encounter the work piece. The neutral species cause undesirable parasitic effects such as etching, oxidation, and film deposition on the walls of the process chamber as well as the surface of the work piece. In conventional plasma-based material modification systems, such parasitic effects are substantial and may result in frequent process excursions and low product yields.